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Share-Based Compensation and Benefit Plans (Tables) | 6 Months Ended
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Jun. 30, 2020
Restricted stock [Member] |
Share-Based Compensation and Benefit Plans |
Summary of activity of share-based compensation and benefit plans | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | For the Three Months Ended | ​ | For the Six Months Ended
​ | ​ | June 30, | ​ | June 30,
​ |  | 2020 |  | 2019 |  | 2020 |  | 2019
Compensation expense for shares issued under the ESPP | ​ | $ | 697 | ​ | $ | 632 | ​ | $ | 1,343 | ​ | $ | 1,209
Income tax benefit from compensation expense related to shares issued under the ESPP | ​ | ​ | 176 | ​ | ​ | 157 | ​ | ​ | 338 | ​ | ​ | 301
Compensation expense for restricted shares awarded | ​ | ​ | 351 | ​ | ​ | 348 | ​ | ​ | 702 | ​ | ​ | 687
Income tax benefit from compensation expense related to restricted awards | ​ | $ | 88 | ​ | $ | 86 | ​ | $ | 177 | ​ | $ | 171
Stock option [Member] |
Share-Based Compensation and Benefit Plans |
Summary of stock options | ​
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Shares | ​ | Weighted- Average
​ | ​ | (in thousands) | ​ | Exercise Price
Outstanding at December 31, 2019 |  | 1,635 | ​ | $ | 218.10
Granted |  | 149 | ​ |  | 384.75
Exercised |  | (121) | ​ |  | 148.80
Forfeited or expired |  | (13) | ​ |  | 293.46
Outstanding at June 30, 2020 |  | 1,650 | ​ | $ | 237.64
Exercisable at June 30, 2020 |  | 1,107 | ​ | $ | 193.01
Black-Scholes option pricing model | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | June 30,
​ |  | 2020 | ​ | 2019
Risk free interest rate |  | 0.96 | % | ​ | 2.44 | %
Expected life |  | 6.2 | Years | ​ | 6.0 | Years
Expected volatility |  | 25.8 | % | ​ | 25.0 | %
Expected dividend yield |  | — | % | ​ | — | %
Summary of activity of share-based compensation and benefit plans | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | For the Three Months Ended | ​ | For the Six Months Ended
​ | ​ | June 30, | ​ | June 30,
​ |  | 2020 |  | 2019 |  | 2020 | ​ | 2019
Compensation expense for stock options awarded | ​ | $ | 4,557 | ​ | $ | 4,611 | ​ | $ | 9,435 | ​ | $ | 9,119
Income tax benefit from compensation expense related to stock options | ​ |  | 1,148 | ​ |  | 1,146 | ​ |  | 2,377 | ​ |  | 2,267

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- Definition Tabular disclosure of share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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